Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . 30 VOLTS Fig. 215-Drop -Measuring the Voltswith a Voltmeter. Exp. 65: Four spools of wireA, B, C, and D, Fig. 215, withresistances of 2, 3, 4, and 6 ohms respectively, are connected in ser-ies and to a battery. The spools may represent lamps, magnets, or MEASUREMENT OE PRESSURE. 241 eVOLTS DROP. Fig. 216.—E and Potential any other electrical devices. When the battery circuit is closedthrough the above circuit, and the voltmeter connected directlyacross its terminals, 30 volts potenti
Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . 30 VOLTS Fig. 215-Drop -Measuring the Voltswith a Voltmeter. Exp. 65: Four spools of wireA, B, C, and D, Fig. 215, withresistances of 2, 3, 4, and 6 ohms respectively, are connected in ser-ies and to a battery. The spools may represent lamps, magnets, or MEASUREMENT OE PRESSURE. 241 eVOLTS DROP. Fig. 216.—E and Potential any other electrical devices. When the battery circuit is closedthrough the above circuit, and the voltmeter connected directlyacross its terminals, 30 volts potential difference is indicated. Thetotal external resistance is 2 -f- 3 -4- 4 -4- 6 = 15 ohms, and the 30volts potential difference indicated by the voltmeter is the pressurecausing the current to flow through this external resistance. Thecurrent is, by Formula (28) 30 -=- 15 = 2 amperes. To measure the proportion of the total P. D., 30 volts, causing the cur-rent to pass through the 2 ohm spool, A, Fig. 215, the voltmeter isplaced in parallel with it, or connected to the points H and K, and in-dicates 4 volts. When the ^ volts dropvoltmeter is connected across .,, .the 3 ohm spool B, 6 volts are M r-dXJMXJv^-indicated. The current is thesame as through spool A, theresistance, however, beingH times as great as A re-quires, also 1J- times thevoltage that A C has 4 ohms, or twicethe res
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